Copy letter, from Sir John Herschel to Wilhelm Struve, dated at Collingwood Copy of a letter. Apologizes for not having written, but has been 'harassed with desultory and importunate calls on [his] name.' Commends Wilhelm Struve on accomplishments at Pulkowa and performance of Repsold instruments. Congratulates Wilhelm Struve on his son Otto Struve. Received Wilhelm Struve's figures on Halley's Comet. Comments on bright stars of variable nature. Estimates 35 or 36 magnetic observatories in the world. 13 July 1840